Memory modules come in a variety of configurations depending on a given application and desired storage capacity. For high-capacity memory modules that employ significant numbers of memory devices, a buffered architecture is often employed. The buffered approach buffers data transferred between the memory devices and a memory controller, thus reducing loading of a data bus to the relatively few buffer devices, rather than the high number of memory devices. Address and control busses are also typically buffered in these systems.
Employing increasing numbers of memory devices on conventional high-capacity memory modules exposes the overall memory to a cumulative yield problem. A significant percentage of conventional memory modules may develop permanent failures at the memory device level after operating in the field for a relatively short duration. Replacing individual devices on a module is generally impractical, resulting in an entire module replacement if the number of failures significantly impact the performance or capacity of the overall memory.